Emulsion explosives are well-known in the art. See, for example, U.S. Pat. Nos. 4,356,044; 4,322,258; 4,141,767; 3,447,978 and 3,161,551. Emulsion explosives are found to have certain advantages over oonventional aqueous slurry explosives, which have a continuous aqueous phase, as described in U.S. Pat. No. 4,141,767.
Emulsion explosives generally are formed at elevated temperatures, which are necessary to form the solution of oxidizer salt(s) in water. It has been found, however, that once the emulsion explosive is formed at the elevated temperature, it should be cooled rapidly to ambient temperature in order to preserve its long-term storage stability. Moreover, where such emulsion explosives are chemically gassed for sensitivity purposes, the formulated emulsion should be cooled quickly to minimize migration and coalescence or escape of the chemically generated gas bubbles within the emulsion. Accordingly, in forming chemically gassed, packaged emulsion explosives, it is desirable to cool each stick package as quickly as possible.
Packaged explosives have been manufactured for many years. For example, dynamites have been paper-wrapped in conventional machines to form symmetrical cylindrical sticks having crimped or "squared" ends that form planer surfaces perpendicular to the axis of the cylindrical stick. Packages in this form are convenient for handling, and when loaded into boreholes, have good end-to-end contact which facilitates stick-to-stick propagation of a detonation. Slurry explosives, which comprise a thickened gel of oxidizer salt solution throughout which a fuel is dispersed or dissolved, have been packaged in a sausage-like form in a flexible tubing such as polyethylene having clipped ends. A process and apparatus for packaging slurry explosives in a sausage-like form is described in U.S. Pat. No. 3,783,735. The clipped ends, however, tend to interfere with close end-to-end contact, and thus clipped polyethylene tubes are not as desirable as crimped paper tubes in assuring reliable detonation propagation from stick to stick in a loaded borehole. More recently, emulsion explosives have been packaged either in crimped paper tubes, similar to that used for packaging dynamite, or in sausage-like clipped tubes, similar to that used for packaging slurry explosives. For certain applications and for the reasons set forth above, it is desirable to package emulsion explosives in symmetrical paper-wrapped cylinders having squared ends formed by crimping or other means.
Emulsion explosives generally require some form of uniform distribution of gas bubbles for adequate detonation sensitivity. A common method of introducing sensitizing gas bubbles is incorporating a uniform distribution of void containing materials, such as glass or plastic microspheres or perlite, throughout the emulsion. These void containing materials will not tend to migrate or coalesce once dispersed throughout the emulsion, and therefore, packaging of emulsions containing these materials is relatively simple.
Another means of sensitizing emulsion explosives is by the introduction of ingredients which react chemically to produce gas bubbles. Chemical gassing is a less expensive means of sensitization than the use of hollow microspheres and is therefore preferred from a cost standpoint. These free, discrete gas bubbles tend to migrate and/or coalesce in the emulsion or escape from the emulsion, however, unless inhibited by the viscosity of the emulsion itself. Because emulsions are relatively fluid at their elevated formulation temperatures, it is important to cool them quickly and render them sufficiently viscous to minimize migration of the gas bubbles. Heretofore, chemically gassed emulsion explosives have been manufactured in sausage-like packages that are filled and cooled quickly to prevent gas migration. Paper wrapping has not been possible, since it requires that the emulsion be handled while still hot, thereby allowing for migration or escape of gas bubbles.
An additional problem with chemically gassed emulsions is that they tend to shrink in volume as they cool from their elevated formulation temperatures. This is because the volume of an individual gas bubble decreases as the temperature decreases. Thus if chemically gassed emulsions are paper wrapped at their elevated formulation temperatures, undesirable shrinkage within the paper package would occur upon cooling. In accordance with the present invention, however, if chemically gassed emulsions are prepackaged in a flexible tubing, preferably under pressure, and cooled prior to paper wrapping, shrinkage within the paper wrapped cartridge essentially is eliminated. A need therefore exists for a method of manufacturing chemically gassed emulsions in symmetrical cylindrical packages, such as paper-wrapped packages having crimped ends.